EP 2 149 651 A1 discloses a system for laying wood floors without using screws, nails and glue, but by interlocking or wedging them. According to the system of the cited patent, inserted at regular distances on parallel sections of a base frame are connecting members adapted to permanently connect the parallel sections with slats arranged orthogonally to the parallel sections and forming a coating. Such connecting members are C-shaped in their side towards the parallel sections and have end hooks to allow both the connecting members and the parallel sections to be joined. On their opposite side with respect to the parallel sections the connecting members have a first pair of opposite central hooks, between which a spacer acting as an abutment is interposed, and a second pair of side hooks facing the respective central hooks. All the hooks are angled at their free ends in order to engage slats through grooves thereof on the opposite side to the one in sight. In particular, the slats have side grooves and bottom grooves, both having undercuts forming dovetail portions which the free ends of both the central hooks and the side hooks respectively abut from opposite sides.
A drawback is related to the configuration of the grooves, in particular of the bottom grooves: the free ends of the side hooks point against the dovetail portion so that they are fixed in the undercut. The slats, where necessary, can be disassembled, although with difficulty, but there is the risk of a rupture of the hooks.
A solution to this problem was already given by the Applicant who has manufactured prismatic-shaped bottom grooves, i.e. without undercut. In this way each side hook disengages easily the slat, thanks to the fact that a joint not difficult to release is not formed as there is no undercut. In this solution the connection is provided only by the central hooks, and this leads to a reduced stability of the slats with a consequent risk of their displacement as a result of loads applied on the coating structure.
Therefore, a drawback of the surface coating structure of the prior art is to not allow a proper engagement between slats and connecting members.
It should also be highlighted that the surface coating structures in question are intended to both horizontal surfaces, such as floors that must withstand loads by their nature, and vertical surfaces, such as those of the facade walls. In the prior art the connecting members, which serve to transmit the load from the slats to the base frame, are made identical in both cases.
The Applicant found that the connecting members need to be most strong in the case where they are used for coating horizontal surfaces, and they may be less robust in the case where they are used for coating vertical surfaces.
In particular, in the first case it would be useful that the slats rest firmly on the connecting members; in the second case it is convenient that the connecting members are made in such a way that their assembly with the parallel sections that constitute the base frame of the surface coating structure is easy, such an assembly being obtained by inserting the connecting members in the parallel sections.
Another feature of this type of surface coating structure must also be considered: flanked slats rest with their adjacent edges on the same connecting members. In order to obtain a proper support, ends of consecutive slats must not stay between a connecting member and the other, so as to be cantilevered between a section of the base frame and the other; on the contrary, the ends of consecutive slats must stay on the same connecting member. Since the consecutive slats are inserted at successive times, it occurs that an angled hook of the pair of central hooks provided on the upper part of the connecting members is in locked position, inside the side groove of the slat, in virtue of the occurred engagement between an end of a first slat and the connecting member. The insertion of a contiguous end of a second slat consecutive to the first one, which would cause the deformation downwards of the angled hook of the connecting member on which the end of the first slat rests, is hindered by the occurred engagement of the end of the first slat: the final result is an uncertain engagement between the contiguous ends of the two consecutive slats because a single hook must operate in the engagement with two different slats at successive times.